Signal generator for electronic commutation of a motor

ABSTRACT

Control signals for electronic commutation of an electric motor have three related frequencies, namely a &#39;&#39;&#39;&#39;synchronous&#39;&#39;&#39;&#39; frequency proportional to the speed of rotation of the motor, a control or &#39;&#39;&#39;&#39;resultant&#39;&#39;&#39;&#39; frequency representing the frequency of pulses controlling commutation of the motor and hence characteristic of the rotation or commutation of the motor field and a &#39;&#39;&#39;&#39;slip&#39;&#39;&#39;&#39; frequency representing the difference between the &#39;&#39;&#39;&#39;resultant&#39;&#39;&#39;&#39; frequency and the &#39;&#39;&#39;&#39;synchronous&#39;&#39;&#39;&#39; frequency and hence characteristic of the &#39;&#39;&#39;&#39;slip&#39;&#39;&#39;&#39; of the rotor of the motor with respect to the rotation or commutation of the motor field. A signal generator for controlling the commutation of an electronically commutated motor comprises means for individually generating two of these three characteristic frequencies and means for electronically deriving the third characteristic from the other two.

United States Patent [151 3,691,438 Favre 14 1 Sept. 12, 1972 [54]SIGNAL GENERATOR FOR 3,323,032 5/1967 Agarwal et al ..3l8/227 x'ELECTRONIC COMMUTATION OF A MOTOR Primary Examiner-Gene Z. Rubinson [72]Inventor Robe" Favre 36 Rue du Sen/an Attorney-Robert E. Burns andEmmanuel J. Lobato 9 9 Lausanne, Switzerland 1 [22] Flled: July 1970Control signals for electronic commutation of an elec- 21 A 1. No.1 52669 tric motor have three related fre uencies, name] a pp 3 q ysynchronousfrequency'proportional to the speed of Related Appliciuollrotation of the motor, a control or resultant [63] Continuation-impartof Ser. No. 674,968, Oct. freqilency reprcsepung the frequency of pulsescon- 12, 1967 abandoned trolling commutat1on of the motor and hencecharacteristic of the rotation or commutation of the motor 521 U.S. c1..318/133, 318/227, 318/230, field and a "Presenting the 318/231 ferencebetween the resultant frequency and the [51] Int CI 02k 29/00synchronous"frequency and hence characteristic of the slip of the to):of the motor with respect to the [58] Field of Search ..3l8/138, 227,230, 231 rotation or commutation of the motor field. A signal [56]References Cited generator for controlling the commutation of anelectronically commutated motor comprises means for in- UNITED STATESPATENTS dividually generating two of these three characteristicfrequencies and means for electronically deriving the 3,387,195 6/1968Plccand et al. ..3l8/227 h f th m t 3,477,002 11/1969 Campbell ..3l8/227thud meter mm er 3,372,323 3/1968 Guyeska ..318/231 X 8 Claims, 4Drawing Figures 5) use/m T mT GEMAATO'? A 2 F/PEQUE/YCY ADDERSZ/PS/GWAI. 9\ GENERATOR TI'I'ITTIT mm MA 0c POWER LOMNUTATOR PATENTEUSE! 12 I972 SHEET 1 0F 2 .S'YNS/GML GE/VEAA TOR SZ/FS/GWAL GE NE EA 70RFREQUENCY ADDER 8 COM/YUM TOR FIG 2 5m SIGNAL GENE/PA TOP PESUUX/VTFREQ. GE/V.

FREQ. D/K" CON/707217271? 0C. POWER F/PEGUEA/O 5087194670? DC POI/E?PATENTED SEP 12 I972 same or 2 SIGNAL GENERATOR FOR ELECTRONICCOMMUTATION OF A MOTOR This application is a continuation-in-part of mycopending application Ser. No. 674,968 filed Oct. 12, 1967 nowabandoned.

The present invention relates to electronic commutation of electricmotors.

Various procedures are known for feeding the windings of an electricmotor from a direct current source by electronic commutation by means ofsuitable switching elements, for example thyristors or transistors,under control of a suitable control circuit for switching thecommutation elements to energize the field windings of the motor inproper sequence and at a selected rate to provide a rotating or movingfield. Control of the commutation is generally provided by a pulsegenerator producing a monophase signal which controls the switchingelements of the commutation circuit. In the case of a polyphase motor,for example a three phase motor, sequential commutation of the motorwindings is provided by means of a suitable form of closed circuitimpulse counter which acts as a distributor to feed the control pulsessequentially and cyclically to the switching elements controlling theseveral phase windings in order to energize the windings in propersequence and proper timed relation to one another.

In a polyphase motor, commutation of the current supplied to the fieldwindings is efi'ected so as to produce a rotating field. Similarly, amoving field for producing rotation of the rotor is provided by thecommutation of a single phase motor. In an induction type motor therotor lags behind the field, i.e., the speed of the rotor is less thanthat of the field. The difference between the field speed and the rotorspeed is referred to as slip. The same is true of a synchronous motorduring starting since the motor has the characteristics of an inductionmotor until it reaches synchronous speed.

As the operations effected by the control signals in the electroniccommutation of an electric motor are a type of logic, it is of interestto note that the control signals have three frequency characteristicsthat may be called the synchronous component, the slip component and theresultant frequency. The synchronouscomponent is proportional to thespeed of the motor while the slip" component is proportional to the slipof the rotor of the motor with respect to the field. The resultantfrequency is proportional to the speed of rotation or commutation of themotor field and represents the sum of the synchronousand slipcomponents. Hence, any one of these three characteristics can be derivedfrom the other two by an arithmetical operation.

A difficulty frequently encountered in the control of an induction motorby electronic commutation is that of maintaining the slip componentwithin limits adapted to the conditions of optimal operation of themotor.

The present invention has for its object a circuit for generatingsignals for the control of electronic commutation of an induction motorcharacterized by the fact that the circuit comprises means forgenerating individually two of the three above mentioned characteristicsof the control signals, namely the synchronouscomponent, the slip"component and the resultan frequency and means for deriving the thirdcharacteristic from the other two by an arithmetical operation effectedelectronically.

The invention will be more fully understood from the followingdescription in conjunction with the accompanying drawings in which:

FIG. 1 is a block diagram of a circuit for generating pilot signals inwhich the synchronous and slip components are generated individually,the resultant frequency being obtained by an electronic addition ofthese two components;

FIG. 2 is a block diagram of a circuit for generating pilot signals inwhich the synchronous" component and the resultant frequency areindividually generated, the slip component being obtained by anelectronic subtraction of the synchronous component from the resultantfrequency;

FIG. 3 is a circuit diagram of the circuit for electronic subtraction ofthe components in accordance with FIG. 2 as represented by the block 3in FIG. 2;

FIG. 4 is a circuit diagram of a pulse generator circuit for generatingthe resultant frequency in accordance with FIG. 2 as represented by theblock 2 in FIG. 2.

In FIG. 2 the circuitry shown in FIG. 3 is represented by the block 3and the circuitry shown in FIG. 4 is represented by the block 2.Corresponding points of connection are indicated by the letters A, B andC respectively. Thus, inputs A and B in block 3 of FIG. 2 correspond toinputs A and B in FIG. 3 while the output C shown in FIGS. 2 and 3 isconnected with the input C of FIG. 4. 1

In the circuit shown in FIG. 1, the motor 0 drives a pulse generator 1which generates pulses in synchronism with the motor and thuscorresponding to the synchronous component. This generator can bedesigned in many ways, particularly by the interaction of an emitter andof a pick up, the interaction being intercepted by a disc which is fixedto the rotor of the motor and is solid except for suitable gaps in itsperiphery in such manner as to deliver as many signals per revolution ofthe motor as there are gaps in the disc. The interaction can bephotoelectric, electromagnetic, capacitive magnetic, etc. For example,the emitter may be in the form of a lamp and the pick up in the form ofa photosensor, for example a photodiode.

Block 2 represents a pulse generator for generating pulse signals at afrequency corresponding to the slip component. The pulse generator maybe of any desired type for generating pulses at a controllable frequencyand may for example comprise a variable frequency multivibrator as inthe pulse generator which is shown in FIG. 4 and will be describedbelow. The frequency of the slip signals is made subject to the speed ofthe motor by an input through channel 6 and is maintained in the rangebest adapted to the prevailing conditions of operation of the motor.

Block 3 comprises a frequency adder for adding the synchronouscomponentreceived from block 1 through channel 5 and the slip component receivedfrom block 2 through channel 7. The sum of these two componentsrepresents the resultant frequency and is directed through channel 8 toblock 4. The circuit may for example be a multivibrator which istriggered both by pulses of the synchronous component and pulses of theslip component so that the output frequency is the sum of the two inputfrequencies. The circuit of block 3 also delivers to block 2 throughchannel 6 a corrective or control signal for regulating the frequency ofthe slip component produced by the pulse generator of block 2 in orderto provide a slip frequency of optimal value for the prevailingoperating conditions of the motor.

Block 4 comprises circuitry for commutating direct current received froma dc power source 40 and feeding the commutated current through channel9 to the field windings of the motor 0. The motor is shown by way ofexample in the drawings as a three phase motor and channel 9 accordinglycomprises a three phase line. With a polyphase motor, the commutationcircuit comprises transistors or other switching elements for each phaseand a distributor for example in the nature of a closed circuit pulsecounter for distributing the pulses received through channel 8sequentially and cyclically to the switching elements of the severalphases so as to control the switching of the respective switchingelements in proper sequence and time relation. With a single phasemotor, such distributor is not required. The block 4 also preferablycomprises an electronic frequency divider which acts proportionally toreduce the frequency received through channel 8 from block 3. Thereduced frequency is utilized to control commutation of the motor. Thispreliminary division of the frequency permits starting with a relativelyhigh frequency having the advantage of reducing the time of response tothe information supplied to block 3 through channels 5 and 7.

Electronic commutation circuitry for polyphase motors is shown forexample in my copending applications Ser. No. 676,871 filed Oct. 20,1967 and Ser. No. 682,176 filed Nov. 13, 1967. Circuitry for theelectronic commutation of single phase motors is shown for example inFavre U. S. Pat. Nos. 3,309,592 and 3,436,631.

In FIG. 2 as in FIG. 1, the block 1 comprises a pulse generator forgenerating pulses at a frequency corresponding to the speed of the motor0 thus producing synchronous component as described above. Block 2represents a pulse generator for producing pulses at a variablefrequency corresponding to the resultant frequency. BLock 3 representscircuitry for processing the information received from blocks 1 and 2and performing a subtraction of the synchronous component from theresultant frequency so as to obtain the slip component which is appliedto the pulse generator 2 through channel 6 so as to correct and controlthe resultant frequency. A branch channel 8 conducts the signals of theresultant frequency to the commutation circuit of block 4 which performsthe same functions as described above in the case of FIG. 1. The controlsignals supplied to block 4 through channel 8 are equidistant, contraryto the case of FIG. 1, which assures a better stability of operationparticularly at low speeds.

FIG. 3 shows a very simple circuit for the electronic subtraction offrequency signals and corresponds to the block 3 in FIG. 2. Thetransistors 10 and 11 with associated components operate as a bistablemultivibrator or flip-flop. When the transistor 10 is conducting, thetransistor 1 1 is nonconducting and conversely when the transistor 11 isconducting the transistor 10 is nonconducting. A pulse received at inputA in FIG. 3 (corresponding to input A of block 3 in FIG. 2) from thesynchronous pulse generator 1 is transmitted through a capacitor 41 anddiode 12 to the collector of the transistor 10 causing it to becomeconductive and thereby causing transistor 11 to be blocked. In similarmanner a pulse received at input B of FIG. 3 (corresponding to input Bof block 3 in FIG. 2) from the resultant frequency pulse generator 2 istransmitted through a capacitor 42 and diode 13 to the collector oftransistor 11 thereby causing it to become conductive and blockingtransistor 10. The diodes l2 and 13 assure a selective effectiveness ofthe signals and wholly decouple the pulse generators from the bistablemultivibrator.

Input B in FIG. 3 is also connected through a capacitor 17 and outputtransistor 16 to an output channel 18 leading to an output terminal C.The emitter of transistor 16 is connected with the emitter of transistor11 while the base of transistor 16 is connected through a resistance 15to the collector of transmitter 11. By reason of its bias, the outputtransistor 16 is normally blocked and can only deliver an output pulseto a channel 18 when it receives through the capacitor 17 a pulse ofresultant frequency from block 2 at a time when the transistor 11 isconducting. If the frequency of the signal of the synchronous componentis equal to the resultant frequency, the pulses received at input A andB alternate with the result that the transistor 1 l is always lookedwhen a pulse is received at input B. Hence, under these conditions, theoutput transistors 16 can not deliver any pulse to the output channel18. If on the other hand, the resultant frequency is higher than thesynchronous component, it happens periodically that two successivepulses are applied to the input 2 without any pulse on the input 1. Thesecond pulse applied at input 2 then finds the transistor 11 conductiveand hence a pulse is delivered by the transistor 16 to the channel 18.It will be seen that the number of pulses delivered to the channel 18 isequal to the number of pulses received at input B from the resultantfrequency generator 2 minus the number of pulses received at input Afrom the synchronous frequency component generator 1. The frequency ofthe pulses delivered to the channel 18 thus represents the slipcomponent. The process of subtraction functions here only in the case ofa resultant frequency higher than the frequency of the synchronouscomponent (positive slip component) which is of interest.

FIG. 4 which corresponds to the block 2 in FIG. 2 shows the circuit of apulse generator for generating signals of the resultant frequency withprovision for correcting the starting frequency of the slip component.The transistors 21 and 22 together with associated components includingcapacitors 26 and 28 and resistors 27 and 29 comprise a multivibrator.The lines 30, 31, 33 and 34 supply fixed potentials from a suitablevoltage source (not shown). The voltages of lines 30, 31, 33 and 34 arearranged in the order of the numbering of the lines, line 30 beinglowest in voltage and line 34 highest. By virtue of the special couplingbetween transistors 21 and 22 comprising the capacitor 28 and resistor27 connected in series and the capacitor 28 and resistor 29 connected inshunt, the multivibrator has a frequency which is variable over a verylarge range. The resistor 27 and capacitor 28 comprise a delay circuitwith a time constant much greater than that of the capacitor 28 and theresistor 29.

The emitters of the transistors 21 and 22 are connected through acapacitor 25 to a voltage supply line 32 which in turn is connectedthrough a resistance 24 to a fixed potential supply 34. With theconnections shown, the frequency of oscillation of the multivibrator isvariable over a very large range as a function of the potential of line32 which depends on the amount of charge of the capacitor 25 and istherefore variable. The voltage supply line 32 is connected through adiode and a resistance 43 to the collector of a transistor 19, the baseof which is connected through a capacitor 44 and a channel 18 with thecollector of the output transistor 16 of the subtraction circuit shownin FIG. 3. The transistor 19 is normally non-conducting, but ismomentarily unblocked by the subtraction pulses received through channel18 from the circuitry shown in FIG. 3. When the transistor 19 isconductive, the potential of the supply line 32 is decreased by thediode 20, becoming conductive so as to discharge the capacitor 25. Thepotential of line 32 and hence the frequency of oscillation of themultivibrator comprising transistors 21 and 22 is varied according tothe frequency of the subtraction pulses (slip component) receivedthrough a channel 18 from the subtraction circuit shown in FIG. 3. Asthe slip component frequency increases, the frequency of oscillation ofthe multivibrator decreases thereby decreasing the frequency of pulsessupplied at the output B of the multivibrator which is connected throughchannel 7 with the input B of the frequency subtractor of FIG. 3 (block3 in FIG. 2) and through channel 8 with the commutation of circuit ofBlock 4 in FIG. 2. A transistor 23 is connected between the line 32 andthe lower voltage supply line 31 of the voltage supply serves to providea limit of the potential of line 32 as a function of adjustment of apotentiometer 35 in its base circuit. The resistor 24 limits the rate ofcharging of the condensor 25 and thus the rate of increase of potentialof line 32 during starting of the motor and between successivesubtraction of pulses.

The operation of the motor and its control circuit is as follows:

At the starting of the motor, the potential of the supply line 32 startsat a value near the potential of supply line 31 which assurs a minimumresultant frequency (slip component) initially in the neighborhood of 4Hz. The values of the resistor 24 and the capacitor 25 determine therate of increase of the potential of line 32 and its resultant inputfrequency 7 through transistor 19 and diode 20, as described above, in amanner to limit the potential of line 32 and thereby retard the rate ofincrease of the resultant frequency.

The normal operating speed of the motor is determined by the lirnitationof the potential of line 32 by the transistor 23 under control of thepotentiometer 35. If an overload on the motor brings about an excessiveslip component, the resulting subtraction pulses acting through thetransistor 19 and diode 20 automatically decrease the operating voltageof the multivibrator and hence the frequency of the multivibrator in amanner to reduce the resultant frequency so as to maintain maximumtorque. The multivibrator shown in FIG. 4 permits variation of frequencyover a very wide range for example, in the ratio of 1/200. The meansdescribed for obtaining this effect can, if desired, be replaced by aunijunction transistor.

By assuring a slip frequency of the motor that is always well adapted tothe conditions of operation, the circuitry according to the presentinvention permits deriving maximum advantage from electronicallycommutated motors for which the peak current is always limited to avalue in the vicinity of the normal current range in order to avoiddamaging transistors or other circuit components.

While preferred embodiments of the invention have been illustrated inthe drawing herein particularly described, it will be understood thatfeatures of the illustrated embodiments are mutually interchangeableinsofar as they are compatible and that other modifications in circuitrymay be made. The invention is hence in no way limited to the illustratedembodiments.

What I claim and desire to secure by Letters Patent 1s:

1. In a signal generator for electronic commutation of a direct currentmotor, the combination of a first pulse generator coupled with saidmotor and producing pulses of a first frequency in synchronism with therotation of said motor, a second pulse generator for producing pulses ofa variable second frequency, said second pulse generator comprising amultivibrator including a voltage responsive delay circuit controllingthe frequency of oscillation of said multivibrator, circuit means forsubtracting the frequency of said pulses produced by said first pulsegenerator from the frequency of the pulses produced by said second pulsegenerator, means responsive to the output of said subtracting means forproducing a voltage having a value varying with the difference betweensaid first and second frequencies, means for applying said voltage tosaid voltage responsive delay circuit to regulate the frequency ofoscillation of said multivibrator to increase the frequency ofoscillation of said multivibrator upon decrease of said difference andto decrease the frequency of oscillation of said multivibrator uponincrease in said difference, means for providing an upper limit of thepotential applied to said voltage responsive delay circuit and therebylimiting the speed of the motor, and means including a frequency dividerfor transmitting pulses of said regulated frequency of saidmultivibrator to said motor.

2. A signal generator for electronic commutation of a direct currentmotor according to claim 1, in which said multivibrator comprises twotransistors and two delay circuits coupling said transistors, one ofsaid delay circuits having a time constant much greater than the other.

3. A signal generator for electronic commutation of a direct currentmotor according to claim 1, in which said potential limiting meanscomprises a transistor and a potentiometer controlling the bias of saidtransistor.

4. A signal generator for electronic commutation of a direct currentmotor according to claim 1, in which said frequency subtracting circuitmeans comprises a bistable circuit including two transistors and anoutput circuit comprising a third transistor coupled to said bistablecircuit, means for applying pulses from said first pulse generator to aninput of said bistable circuit and means for applying pulses from saidsecond pulse generator to said third transistor.

5. In a signal generator for electronic commutation of an inductionmotor having field windings and a rotor and electronic commutating meansfor supplying current to said field windings to produce a moving field,the combination of a first pulse generator actuated by the rotor of saidmotor and producing pulses at a frequency which is a function of motorspeed, a second pulse generator supplying pulses to said commutatingmeans to control the rate of commutation of said commovement of saidfield, the frequency of said second pulse generator being variable andcontrollable, the speed of rotation of said rotor being less than thespeed of movement of said field by an amount designated slip, means forsensing said slip, and means responsive to said slip sensing means tocontrol the frequency of said second pulse generating means to vary saidfrequency mutating means and thereby control the speed of inversely withsaid slip and thereby maintain said slip within selected limits,saidslip sensing means comprising electronic means for subtracting thefrequency of pulses produced by said first pulse generator from thefrequency of pulses produced by said second pulse generator andproducing a signal having a frequency proportional in value to thedifference of said frequencies, said subtracting means comprising abistable multivibrator controlled by pulses from said first pulsegenerator, and a transistor the conduction of which is controlled bysaid multivibrator and pulses from said second pulse generator.

6. A signal generator according to claim 5, comprising means forlimiting the frequency of said second pulse generator to a selectedmaximum value, thereby determining the normal running speed of saidmotor.

7. A signal generator according to claim 5, in which second pulsegenerator comprises a variable frequency multivibrator the frequency ofwhich is variable as a function of an applied voltage and in which saidmeans to control the frequency of said second pulse generator comprisesmeans for varying said applied voltage as a function of the differencebetween the frequencies of said second pulse generator and said secondpulse generator.

8. A signal generator according to claim 9, comprising means forlimiting said applied voltage and thereby limiting the frequency of saidvariable frequency multivibrator, said voltage limiting means comprisinga transistor and a potentiometer controlling the bias of saidtransistor.

1. In a signal generator for electronic commutation of a direct current motor, the combination of a first pulse generator coupled with said motor and producing pulses of a first frequency in synchronism with the rotation of said motor, a second pulse generator for producing pulses of a variable second frequency, said second pulse generator comprising a multivibrator including a voltage responsive delay circuit controlling the frequency of oscillation of said multivibrator, circuit means for subtracting the frequency of said pulses produced by said first pulse generator from the frequency of the pulses produced by said second pulse generator, means responsive to the output of said subtracting means for producing a voltage having a value varying with the difference between said first and second frequencies, means for applying said voltage to said voltage responsive delay circuit to regulate the frequency of oscillation of said multivibrator to increase the frequency of oscillation of said multivibrator upon decrease of said difference and to decrease the frequency of oscillation of said multivibrator upon increase in said difference, means for providing an upper limit of the potential applied to said voltage responsive delay circuit and thereby limiting the speed of the motor, and means including a frequency divider for transmitting pulses of said regulated frequency of said multivibrator to said motor.
 2. A signal generator for electronic commutation of a direct current motor according to claim 1, in which said multivibrator comprises two transistors and two delay circuits coupling said transistors, one of said delay circuits having a time constant much greater than the other.
 3. A signal generator for electronic commutation of a direct current motor according to claim 1, in which said potential limiting means comprises a transistor and a potentiometer controlling the bias of said transistor.
 4. A signal generator for electronic commutation of a direct current motor according to claim 1, in which said frequency subtracting circuit means comprises a bistable circuit including two transistors and an output circuit comprising a third transistor coupled to said bistable circuit, means for applying pulses from said first pulse generator to an input of said bistable circuit and means for applying pulses from said second pulse generator to said third transistor.
 5. In a signal generator for electronic commutation of an induction motor having field windings and a rotor and electronic commutating means for supplying current to said field windings to produce a moving field, the combination of a first pulse generator actuated by the rotor of said motor and producing pulses at a frequency which is a function of motor speed, a second pulse generator supplying pulses to said commutating means to control the rate of commutation of said commutating means and thereby control the speed of movement of said field, the frequency of said second pulse generator being variable and controllable, the speed of rotation of said rotor being less than the speed of movement of said field by an amount designated slip, means for sensing said slip, and means responsive to said slip sensing means to control the frequency of said second pulse generating means to vary said frequency inversely with said slip and thereby maintain said slip within selected limits,said slip sensing means comprising electronic means for subtracting the frequency of pulses produced by said firsT pulse generator from the frequency of pulses produced by said second pulse generator and producing a signal having a frequency proportional in value to the difference of said frequencies, said subtracting means comprising a bistable multivibrator controlled by pulses from said first pulse generator, and a transistor the conduction of which is controlled by said multivibrator and pulses from said second pulse generator.
 6. A signal generator according to claim 5, comprising means for limiting the frequency of said second pulse generator to a selected maximum value, thereby determining the normal running speed of said motor.
 7. A signal generator according to claim 5, in which second pulse generator comprises a variable frequency multivibrator the frequency of which is variable as a function of an applied voltage and in which said means to control the frequency of said second pulse generator comprises means for varying said applied voltage as a function of the difference between the frequencies of said second pulse generator and said second pulse generator.
 8. A signal generator according to claim 9, comprising means for limiting said applied voltage and thereby limiting the frequency of said variable frequency multivibrator, said voltage limiting means comprising a transistor and a potentiometer controlling the bias of said transistor. 